Electrical machining involves machining metal materials by melting them in electrolyte or by directly etching them by electricity. Electrical discharge machining (EDM) is a non-contact machining method; that is, there is always a gap between the tool and the workpiece such that there is no mechanical force on the workpiece. Thus, EDM is suitable for machining delicate, tiny workpieces and complexly shaped workpieces, thin walls of which are easily misshaped.
At present, EDM is based on etching by electrical pulse discharging. The tool and the workpiece are electrically connected to each side of the pulse power, respectively. The difference between EDM and electrolytic machining is that the tool, one electrode, is consumed during machining. Therefore, the material used for the electrode and the machining parameters should be chosen carefully and the size of the electrode should also be designed reasonably to decrease machining inaccuracy caused by the consumption of the electrode.
However, since the gap for electrical discharging needs to be very small and since the tool and the workpiece are constantly being etched away during machining, discharging quickly ceases because the gap widens. Therefore, the machining system needs to have a server control feeding system with high accuracy to constantly feed the electrode and to automatically keep the discharging gap at a best distance.
Reference is made to FIGS. 1 to 3, which illustrate conventional power conversion apparatuses for electrical discharge machining. Since the linear power converter is used as the main structure in the conventional power conversion apparatuses for electrical discharge machining, the output voltage and current are adjusted by using power resistor D or power transistor E working in the active region to make the voltage big enough to discharge to the workpiece A. Hence, these circuits each have low power conversion efficiency and a large circuit footprint; therefore, they are unfavorable in the industry.
Reference is made to FIG. 4, which illustrates a circuit diagram of a switching power converter. If the switching power converter B is used alone, although high power conversion efficiency and a smaller size can be achieved, desirable load current cannot be obtained, causing the slow dynamic response of the switching power converter.
In summary, the power conversion efficiency of the linear power converters is not sufficient, so the size of the power conversion apparatus of the machine becomes quite big. Moreover, although using the switching power converter alone can improve the power conversion efficiency and decrease the size of the power conversion apparatus, it cannot effectively improve its dynamic response to a sudden change in load current.